(421ac) Understanding the Molecular Mechanisms of Lipid Droplet Formation and Lipolysis In Fission Yeast for Biodiesel Production

Lipid droplets are hypothesized to be storage depots for neutral lipids, the precursors for biodiesel fuels. The interplay between the formation (biogenesis) and breakdown (lipolysis) of lipid droplets is of key importance for harnessing model organisms to produce biodiesel fuels. We use video confocal microscopy to quantify the biogenesis, movement, and lipolysis of lipid droplets throughout the cell cycle of the fission yeast Schizosaccharomyces pombe in log growth phase. The volume changes of existing lipid droplets dominate over both the formation of new lipid droplets and the complete lipolysis of existing droplets. This indicates that addition of materials to pre-existing lipid droplets is favored over the build up and release of neutral lipids from the endoplasmic reticulum (ER). Even so, biogenesis events were observed and quantified by dual labeling of lipid droplets and the endoplasmic reticulum. Each biogenesis event shows different time scales of intensity increase and droplet release from the ER. This is a function of the cell cycle stage with droplets forming between S and G2 phases persisting where those formed during M phase fluctuating in intensity around the threshold value. Pre-existing small droplets are most prevalent. They have the largest fluctuations in effective size, but rarely grow to the diameter of the largest droplets in the cells. Thus, there seems to be a critical size for most droplets. The largest droplets appear to arise from fission events. Thus, fission yeast cells have the most material for biodiesel precursors in G2/M/G1 stages of the cell cycle. Future work involves arresting the yeast at these stages of the cycle for maximum neutral lipid production.